BELLINGHAM — Fluctuations in solar radiation could mean colder weather in the decades ahead, despite all the talk about global warming, retired Western Washington University geologist Don Easterbrook said Tuesday.

Easterbrook is convinced that the threat of global warming from mankind’s carbon dioxide pollution is overblown.

In a campus lecture, he cited centuries of climate data in an effort to convince a somewhat skeptical audience that carbon dioxide’s impact on climate is being much exaggerated by former U.S. Vice President Al Gore and by scientists who appear to have won the debate over global warming.

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“Despite all you hear about the debate being over, the debate is just starting,” Easterbrook said.

30-YEAR TREND

Easterbrook doesn’t deny that the Earth’s climate has been warming slowly since about 1980. But he argued that this warming trend fits a longstanding pattern of warming and cooling cycles that last roughly 30 years. Sunspot activity and other solar changes appear to explain the 30-year cycles, he said.

If that pattern persists, the earth could now be close to the next 30-year cooling cycle, Easterbrook said.

He noted that the 2007-08 winter set records for cold and snow in many parts of the globe. According to the data he displayed, the Earth’s temperature hit a peak in 1998 and has been steady or slightly cooler since then.

“One cold winter doesn’t mean much of anything,” he said. “A 10-year trend is interesting.”

He contended that warming periods appear to match periods of sunspot activity, which currently is at a low point.

Easterbrook noted that astrophysicists have been expecting that activity to begin increasing soon, but so far it has not.

Prolonged periods of low activity could lead to a dramatic cooling such as occurred in Europe during the so-called “Little Ice Age,” a term loosely used to describe cooler weather in the 14th to 19th centuries, Easterbrook said.